During the testing-of gas turbine engines it is often necessary to measure the pressure and temperature of the gas flow through the engine. Suitably positioned sets of pressure and temperature sensors are used to indicate circumferential and radial pressure and temperature profiles respectively at various axial positions throughout the engine. The sensors are mounted either on leading edges of existing engine components or in the absence of suitable hardware on purpose design poles, known as rakes, which slot into the engine.
Generally pressures are measured using pitot tubes and temperatures are measured using thermocouples. In conventional rakes the pitot tubes or thermocouples are mounted forward of the rake body and each is surrounded by a shroud. The shroud defines a cavity around the pitot tube or thermocouple through which a proportion of the gas flow passes. The shroud reduces flow incidence angle sensitivity and provides a measure of environmental protection.
A problem with conventional rakes is that the shrouds are difficult to manufacture and as they protrude forward of the rake body they are vulnerable. Shrouds have been damaged during installation into or removal from a test engine and difficulties have been encountered in repairing the damaged shrouds.